Hello Gian Paolo,
Please excuse me for the delay.
About the refresh of the calculated fields, with the current implementation of the pivot grid the calculated fields should be set before the ItemsSource setting. After this they can't be refresh unless you refresh the source as in your case.
As for expanding the collapsed nodes, doing this via a style doesn't work because the IsExpanded property is set in code which has a higher priority than a style setter. In order to achieve this requirement you can get the TreeGridRowGroupHeader elements in code and set their isExpanded property. Here is an example in code:
sender, RoutedEventArgs e)
I hope that helps.
Want to extend the target reach of your WPF applications, leveraging iOS, Android, and UWP? Try UI for Xamarin
, a suite of polished and feature-rich components for the Xamarin framework, which allow you to write beautiful native mobile apps using a single shared C# codebase.